In prior art communication satellites, functionally a single power bus has been used to power all on board loads including communications amplifiers and so called "housekeeping" loads, such as the attitude control, command, telemetry and thermal, and power subsystems. The bus receives power during daylight hours from a solar array producing typically between 23 and 36 volts. There are actually typically two arrays, one on either side of the satellite, but both are connected to the bus so that functionally the arrangement can be treated as one array. A battery and battery charger are connected in series between the bus and spacecraft ground. The battery is charged during the day and produces power to power spacecraft loads at night. Some spacecraft loads, particularly amplifiers, in the interest of higher efficiency and reduced weight require more voltage than 23 to 36 volts and tighter tolerances, 100 volts.+-.2 volts being exemplary. The prior art system typically employs voltage boosters and voltage regulators to provide the elevated tighter tolerance voltage. To avoid the possibility of malfunction due to failure, typically the battery, battery charger, voltage regulator and voltage booster are all duplicated. Such voltage boosters, voltage regulators, batteries and battery chargers are costly in terms of weight, volume and money. One might consider utilizing a 100 volt bus to replace the 35 volt bus. This would require the use of 100 volt batteries, however, which are not practical.
In the space orbit used by communications satellites, there are only two periods of 44 days each in which the satellite is not illuminated for 24 hours. On these two 44 day periods the satellite is not illuminated for times ranging from two minutes to 72 minutes. In certain satellite systems not all loads are required to be powered during the night periods. Particularly the communications amplifiers which require the tightest tolerance, highest voltage and most current, do not need to be operated at night.